Preparation

1. 1. Preheat oven to 350°F with a rack in the middle position. Line a 13 x 9-inch pan with foil, making sure to leave some overhang. Grease with butter and reserve.
2. 2. In a medium saucepan, heat the butter over medium-low heat, until just melted. Remove from heat and stir in the peanut butter.
3. 3. Insert the chopping blade into the work bowl of the food processor. Add 1 cup of the peanuts and pulse to roughly chop. Remove and reserve. Add the sugar, baking powder, salt, eggs, and vanilla extract to the work bowl. Process on Low until creamy, scraping down bowl as necessary. With the machine running, add the butter mixture in a steady stream through the feed tube, processing until incorporated. Stop and scrape down the sides of the bowl. Sift in the flour and process on Mix until flour disappears. Carefully remove chopping blade and fold in 1 cup reserved, chopped peanuts.
4. 4. Scrape batter into prepared pan and spread into corners of pan, smoothing into an even layer. Drop the warmed fruit jam by the teaspoon, distributing it over the surface. Draw the tip of a knife through the jam to create swirls. Scatter remaining peanuts over the top and sprinkle with flake sea salt.
5. 5. Bake until center is set and a toothpick or cake tester comes out clean, about 35 to 40 minutes, rotating the pan halfway through baking. Do not overbake. Remove from oven and set on wire rack. Let cool completely in pan.
6. 6. To serve, use the foil overhang to lift the bar out of baking pan and transfer to a cutting board.Remove foil and cut into 24